Phosphine complexes of transition metals have been widely employed as soluble catalysts for hydrogenation of carbon to carbon double bonds. Particularly useful and widely studied have been phosphine complexes of rhodium (I) such as Rh(PPh.sub.3).sub.3 Cl, which was described in some detail by Wilkinson and co-workers, e.g., Osborne et al. J. Chem. Soc. Sect. A, 1711 (1966) and has since been very thoroughly studied. Detailed reviews of these topics have appeared (e.g. Harmon et al. Chem. Reviews 73, 21 (1973); B. R. James, Homogeneous Hydrogenation).
When the (PPh.sub.3) moiety of the above-mentioned transition metal complex is replaced by a chiral tertiary phosphine, hydrogenation of a prochiral olefin leads to an excess of one enantiomer of the saturated hydrogenation product. Enantioselective hydrogenation of alpha- and beta-phenyl acrylic acids and alpha-acylamido-beta-phenyl acrylic acids employing chiral tertiary phosphines has been disclosed by Knowles et al. Chem. Tech. 590 (1972) and references therein; Morrison et al., J. Amer. Chem. Soc. 93, 1301 (1971); Kagan et al., J. Amer. Chem. Soc. 94, 6429 (1972) and references therein.
A typical example of such a catalyst is the rhodium (I) complex of neomenthyldiphenylphosphine (1S, 2S, 5R-1-diphenylphosphino-2-isopropyl-5-methyl cyclohexane) described by Morrison et al., supra. Further discussion of these topics may be found, e.g., in Scott and Valentine, Science 184, 943 (1974). In addition, two processes for the enantioselective hydrogenations of alpha-acylamido-beta-phenyl acrylic acids are disclosed and claimed in German Offenlegungschrifts Nos. 2,123,063 (Dec. 2, 1971) and 2,161,200 (June 22, 1972).
Other references pertaining to asymmetric hydrogenation are (1) Knowles et al., J. Am. Chem. Soc. 97, 2567 (1975) relating to asymmetric hydrogenation of substituted amino acids and .alpha.-phenyl acrylic acid; (2) Knowles et al. (appearing in Advan. Chem. Soc. 132, (1974) pp 274-282 where optically active amino acids are prepared by asymmetric hydrogenation employing a rhodium-chiral phosphine catalyst; (3) Solodar, U.S. Pat. No. 3,883,580 discloses the asymmetric reduction of ketones to form optically active secondary alcohol employing a Group VIII metal coordination complex catalyst; and (4) Knowles et al., U.S. Pat. No. 3,849,480 discloses and claims the selective hydrogenation of a substituted or unsubstituted olefin employing as catalyst a coordination complex of a metal. The reference does not disclose homogeneous enantioselective hydrogenations of acrylic acids within the scope of formulas II and III.